This paper presents a study about learning and the problem solving process identified among junior high school pupils participating in robotics projects in the Lego Mindstorm environment. The research was guided by the following questions: (1) How do pupils come up with inventive solutions to problems in the context of robotics activities? (2) What type of knowledge pupils address in working on robotics projects? and (3) How do pupils regard or exploit informal instruction of concepts in science, technology and problem solving within a project-based program? Data collection was made through observations in the class, interviews with the pupils, observations of the artifacts the pupils had constructed, and analyses of their reflections on each project. The study revealed that the pupils had often come up with inventive solutions to problems they tackled by intuitively using diverse kinds of heuristic searches. However, they encountered difficulties in reflecting on the problem solving process they had used. In robotics projects, the pupils deal primarily with qualitative knowledge, namely, the ability to identify specific phenomena in a system or factors that affect system performance. The study also showed that pupils are likely to benefit from implementing informal instruction on concepts in science, technology and problem solving into a project-based program. This type of instruction should take place in the context of pupils' work on their projects, and adopt a qualitative approach rather than try to communicate in the class procedural knowledge learned by rote.